Not sure about this particular experiment, but neutrino detectors are usually deep underground and trying to find a tiny tiny spark of Cherenkov radiation or other effects.
I'm guessing the blue colour is simply paint.

Yup, it's basically the underwater version of sonic booms. Pretty cool stuff

I've seen it from afar and it is indeed a bright blue.

Edit: I don't think that is what we are see here though. It looks like the water itself might have something added to it. There are several elements that absorb neutrons. Such as boron but I'm unsure what color it would be dissolved in water. I inhaled boron gas when I was on the first crew into the containment building at a shutdown. Had to stay at decon until it was out of my lungs.

I saw the spent fuel pool at a nuke from over a hundred feet. It was low light and you could clearly see the blue glow from the spent fuel rods. We were just passing through so it was a quick look to the work site and back from it.

I've also seen a reactor shutdown with the fuel rods exposed in preparation for a fuel shuffle. There may have been a glow but all the lights were on so it would have been washed away.

Yup, pretty much the only kind of radiation we can see without melting your eyeballs.

Fun fact, you can totally swim in that pool. Don’t go too deep but it’s cleaner and safer than your average public pool.

Thats cool as fuck, thanks for explaining!

I mean... I'm not saying that isn't happening but also water is just blue.